The present invention is directed to an apparatus for the measurement of the shape profile and velocity of an individual particle or an individual droplet of a liquid, and also to a beam divider for use in such an apparatus.
There has been developed an apparatus for measuring various characteristics of a droplet of a liquid, such as a droplet of ink for an ink printer. This apparatus is described in detail in the application for U.S. Letters Patent of Tzong-Shyng Leu, Ser. No. 09/215,018, filed Dec. 17, 1998. In general, this apparatus comprises a laser for generating and projecting a beam of light along a path. Along the path of the beam of light is a lens or a lens combined with a set of knife edges which forms the beam into the shape of a thin sheet at a focal point beyond the lens. Also along the path of the beam is a photodetector for receiving the beam and providing an electrical signal corresponding to the light received. Adjacent the path of the beam is means for projecting a droplet of a liquid through the sheet of the beam. The droplet passing through the beam of light varies the amount of light receiving by the photodetector which generates a corresponding signal. From the signal various characteristics of the droplet, such as size and shape, can be determined. However, for various purposes, it would be desirable to be able to measure the velocity of the droplet.
One aspect of the present invention is an apparatus for measuring the velocity of a droplet of a liquid. The apparatus includes means for generating and projecting a beam of light along a first path. Along the first beam path is means for dividing the beam into two separate beams extending along separate second and third paths. Means is adjacent the two beams for projecting a droplet of a liquid through both of the beams. Means is also provided to detect the two beams after the droplet has passed therethrough to provide electrical signals from which the velocity of the droplet can be determined.
Another aspect of the present invention is a beam divider which can be used in the apparatus for measuring the velocity of a droplet. The beam divider includes a body of a light transparent material having two light receiving surfaces. The light receiving surfaces are at an angle with respect to each other and extend from a common point to form a V. The body also includes two light emitting surfaces. Each of the light emitting surfaces is spaced from and parallel to a separate light receiving surface.